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排序方式: 共有248条查询结果,搜索用时 15 毫秒
241.
In this work, we found that MCM-41 prepared using cetyltrimethyl ammonium bromide (CTAB) as the template could be used as a heterogeneous catalyst for the reaction of methanol with propylene oxide to produce propylene glycol methyl ether. 1-Methoxy-2-propanol was the predominant product. The influence of ratio of the reactants, reaction temperature, and time on the yield and selectivity was studied. The as-prepared MCM-41 proved to be an efficient and reusable catalyst, and the separation of the catalyst form the product was very easy.
242.
Zaheer Ahmad Zahoor H. Farooqi Khalid Mohammad 《Journal of Dispersion Science and Technology》2013,34(2):191-199
The interactions of triblock copolymers (TBP) with ionic surfactants were studied employing surface tensiometry, electrical conductivity, steady-state fluorescence (SSF), and dynamic light scattering (DLS) techniques. An increasing trend in the critical micelle concentration (CMC) of SDS/CTAB in the presence of triblock copolymers was observed especially at higher polymer to surfactant ratio. The delay in the CMC of surfactants was more pronounced in the presence of E48B10E48 possibly due to its less hydrophobic nature. The negative values of free energy of micellization (ΔGm) both in case of SDS and CTAB confirmed the spontaneity of the processes. The aggregation number (Nagg) and hydrodynamic radius (Rh) of polymer/surfactant mixed systems were determined by SSF and DLS. The suppression of the surfactant micelle size in the presence of TBP was confirmed by SSF and DLS studies. 相似文献
243.
Mohammad Ilyas Maqsood Ahmad Malik E. H. Al-Mossalamy 《Journal of Dispersion Science and Technology》2013,34(1):50-56
Diperiodatoargentate(III) (DPA) was used as an oxidizing titrant in the spectrophotometric degradation of D-galactose for the first time. The kinetics is based on the reduction of silver(III) to silver(I) by D-galactose at specified experimental conditions. Effects of added [H+] and [periodate] have also been investigated. The premicellar environment of cetyltrimethylammonium bromide (CTAB) and sodiumdodecyl sulphate (SDS) strongly inhibits the reaction rate. The observed rate constant is strongly affected by [CTAB] and [SDS] changes for [surfactant] <cmc. Surfactant concentration range above the cmc does not influence the reaction rate. The monoperiodatoargentate(III) ions act as an active oxidant in comparison to that of DPA. A suitable mechanism involving a two-electron transfer from D-galactose to the silver(III) species has been proposed and hence a corresponding rate equation has been derived. 相似文献
244.
Xuezhen Ren Ganzuo Li HongLi Wang Yanlian Guan 《Journal of Dispersion Science and Technology》2013,34(3-4):263-272
The activity and kinetic characteristics of glucoamylase has been investigated in W/0 microemulsion systems of AOT/isooctane/buffer, CTAB/isooctane/l-pentanol/buffer and TX-100/ibooctane/I-pentanol/buffer, and compared with that in aquous solution. The effect of various parameters, such as pH optimum, To ptimum and water content, on the activity of the enzyme in microemulsion was determined. The results obtained show that the structure of the microemulsion has strong effect on enzyme activity compared to the kcat, in aquous solution, the apparent turnover number k'cat values were decreased in AOT, TX- 100 based system, and in creased in CTAB based system. 相似文献
245.
Hisham J. Y. El‐Aila 《Journal of Dispersion Science and Technology》2013,34(6):927-931
The kinetic complex formation of 0.001 M 2‐nitroso‐1‐naphthol (NAPH)with 0.01 M cobalt (II) ion (Co2+) in aqueous in presence of 0.02 M NaOH at 30°C in aqueous and/or in and 0.002 M cetyltrimethylammonium bromide (CTAB) have been studied using spectrophotometer at 430 nm. The present data showed that the reaction is first‐order with respect to [Co2+]T and NAPH. Also, k obs have constant values within concentration 0.015–0.05 M of NaOH and decreases with increase of concentration of CTAB to 0.002 M, then, k obs have constant values up to 0.005 M. The rate of the reaction in the presence of micelles has been explained with the pseudo‐phase model of the kinetics. Association constants of Co2+ and NAPH to CTAB micelle have been calculated. The activation parameters ΔH* and ΔS* have been obtained. The increase of reaction rate with sodium benzoate (C7H5O2Na) also has been discussed. 相似文献
246.
The formation process of spindle 2-FeOOH particles obtained through the hydrolysis of FeCl3 solutions has been investigated by means of TEM and XRD. The effect of surfactant-Hexadecyl trimethyl ammonium bromide(CTAB) on this process has also been studied. The results show that growth of the needle-like pre-particles is based on the aggregation process, when there is no CTAB in the FeCl3 solution. Once CTAB was added, 2-FeOOH nuclies would grow up through the diffusion mechanism. The2-FeOOH particles were smaller and uniform under the effect of CTAB. The spindle and needle-like 2-FeOOH particles with different axis ratios can be synthesized by controlling the reaction parameters such as the concentration of the original FeCl3 solution and aging temperature. 相似文献
247.
对微环境敏感的系列双亲卟啉的光谱研究 总被引:2,自引:0,他引:2
研究了系列双亲卟啉(四苯酚基卟啉P0及其烷氧基衍生物P1,P2,P3)在不同微环境下的电子吸收光谱和荧光发射及荧光激发光谱.研究发现,卟啉在THF溶液中以单体形式存在,并且其侧链取代基对卟啉电子态的影响很小;然而卟啉在CTAB胶束溶液中的光谱特性却表现出很大差异,由此分析了不同侧链取代基对卟啉分子聚集行为和定位性质的影响,初步解释了卟啉在CTAB胶束溶液中随体系pH值改变而发生的荧光猝灭现象. 相似文献
248.
用CPMG脉冲序列测定了表面活性剂十六烷基三甲基溴化铵(CTAB)分子中的氮甲基(N-CH3)质子的横向弛豫时间(T2表观),并发现测得的T2表观\}与序列中的重聚脉冲间隔时间的一半τ cp有关,说明存在横向弛豫分散现象. 当在τcp≤1 ms时,T2表观与τ2cp}呈线性关系;而当τcp≥4.6 ms时,T2表观变得与τcp无关. 利用Luz-Meiboom两体化学交换模型计算了不同浓度的CTAB溶液中的N-CH3质子的本征横向弛豫时间(T2本征)和化学交换速率kex,发现kex与T2本征和自扩散系数D一样,在临界胶束浓度(CMC)附近发生突变. 这个突变反映了CTAB分子在从单体到胶束的转变过程中其动力学特性发生了改变. 相似文献